Self-indicating thyratron



Oct. 24, 1961 M. YARMOVSKY SELF-INDICATING THYRATRON Filed NOV. 14, 1958 INVENTOR. MAX YARMOVSKY BY 5 m, Mica);

ATTORNEYS 3,605,925 SELF-INDICATING THYRATRON Max Yarmovsky, Livingston, N..l., assignor to Tang-Sol Electric Inc, a corporation of Delaware Filed Nov. 14, 1958, Ser. No. 773,907 Claims. (Cl. 313-197) This invention relates to a gaseous discharge device which is designed primarily for indicating the presence of a voltage or current in an electric circuit. It has particular reference to a sub-miniature tube which is normally non-conducting but which can be controlled to conduct by a short voltage pulse of three to five volts.

Many indicator tubes have been designed and used in complicated circuits, such as computer circuits, in order to indicate the presence of a voltage or current above a predetermined maximum. For the most part these tubes have been small diodes filled with neon gas. As is well known, a voltage of at least 85 volts is required to trigger these devices and after being triggered the voltage across the tube terminals drops to about 60 volts. Various types of circuits can be designed to make use of these diodes, but the greatest disadvantage inherent in these and other prior art tubes is the variable nature of their operating characteristics. So far as is known, all of these indicator tubes have contained electrode coatings of low work function, such as barium oxide and strontium oxide. The use of these substances lowers the triggering voltage but makes the tube sensitive to ambient light and other photon emission. The device of the present invention contains electrodes which have metal surfaces only and therefore the triggering voltage is practically unaifected by ambient light.

The electrode assembly is such that the discharge occurs only near one end of the tube, thereby providing for end-on viewing. The device also contains a novel type of insulator between the control electrode and the anode for permitting cathodic sputtering during conditioning of the cathode surface without production of leakage paths between any of the electrodes.

One of the objects of this invention is to provide an improved self-indicating thyratron which avoids one or more of the disadvantages and limitations of prior art discharge devices.

Another object of the invention is to reduce the voltage variation necessary to cause conduction between the anode and cathode.

Another object of the invention is to provide an indicating device which concentrates the visible discharge in one predetermined area.

Another object of the invention is to provide a discharge device which can be triggered by transistors and other low voltage circuits.

Another object of the invention is to provide a thyratron indicator tube which is always ready for operation without a warm up period.

Another object of the invention is to provide a discharge device which is practically insensitive to photon radiation.

The invention comprises a three electrode cold cathode gas-filled discharge device which includes a carbon anode, a tubular insulator surrounding the anode except for one end which is exposed, and a tubular control electrode or grid which surrounds the insulator. This assembly is positioned within a central hole in a flat disc cathode. The cathode is made with two metal surfaces, generally having a molybdenum disc on the surface facing the exposed end of the anode. The remainder of the cathode is made of nickel.

For a better understanding of the present invention, together with other and further objects thereof, refer- 7 3,005,925 Patented Oct. 24, 1961 ence is made to the following description taken in connection with the accompanying drawings.

FIG. 1 is a cross sectional view of the discharge devlce;

FIG. 2 is a cross sectional view taken along line 22 of FIG. 1;

FIG. 3 is a cross sectional view similar to FIG. 2 but taken along line 33 of FIG. 1; and

FIG. 4 is a schematic diagram of connections showing how the discharge device may be used as a circuit indicator.

Referring now to FIGS. 1, 2 and 3, the discharge device, which is preferably of sub-miniature size, includes an envelope 10 of insulating material, such as glass having a transparent end portion 11. Within the envelope and axially aligned is a carbon or graphite anode 12 connected to a lead-in conductor 13 which is sealed in the envelope for exterior connection. A tubular insulator 14 surrounds the anode and is sealed around the conductor 13 at its lower end portion 15. Insulator 14, which may be of glass, is flared at the top portion where the anode extends into the discharge space.

Surrounding the insulator 14 is a conductive tube 16 which serves as a grid to control the conduction between the anode and a cathode. During the operation of the device a uniform field is created between the anode and grid. Electrode 16, which may be of nickel, is connected by a strap 17 to a lead-in conductor 18 which is sealed in the envelope for connection to an external circuit. Conductor 18 is surrounded by a tubular insulator 20 forpreventing a discharge in the lower portion of the tube.

A cathode 21 is formed with elements 22 and 23. The cathode is in the form of a disc with a central hole 24 within which is the anode and control grid assembly. The cathode is connected by straps 25 to a lead-in conductor 26 similar to conductor 18 which is sealed in the envelope for external connection. Conductor 26 is also surrounded by an insulating tube 27 which prevents conduction in the lower portion of the envelope space.

In order to concentrate the gaseous discharge to one particular space within the envelope so that the discharge may be viewed through the end portion 11, the cathode 21 is constructed with the element 22 of a metal such as molybdenum on its top surface to thereby present a material with low work function to the space between the cathode and anode. The remainder 23 of the cathode structure is made of a material having a higher work function such as nickel and the periphery of the nickel disc is turned over in a downward direction to eliminate sharp edges from the discharge space.

Near the seal end of the tube a mica spacer 28 is positioned in order to segregate the deposits of getter material which may be exploded from a getter capsule (not shown) below this partition. The mica spacer, however, is not necessary and the discharge device will function without this component.

It has been found advisable to include a radioactive material within the envelope. The radioactive material may be a solid such as a radium salt or it may be a radioactive gas such as Kyrpton at a pressure of about 20 mms. This gas provides sufiiicient ioniziation to insure easy starting at a constant predetermined control voltage.

The discharge device may be used in a number of circuits, the one shown in FIG. 4 being typical of its application. The discharge device is supplied with an anode potential supply 30 of about volts in series with a resistor 31 of 5000 ohms. The negative terminal of the potential source 30 is connected to the cathode 21. In order to stabilize the static potential on the control electrode 16 a voltage divider 32 is connected between the anode and the cathode and an adjustable contact point 33 is connected to the control electrode. In one practical application of the invention the potential of the control electrode was maintained at 102 volts. The input circuit includes input terminals 34, a blocking capacitor 35, and a limiting resistor 36 which may be of the order of 100,000 ohms. In this circuit an input pulse of 5 volts positive will always trigger the tube and provide conduction between the anode and cathode and the production of a visible discharge between the top surface of the cathode 21 and the exposed portion of the anode 12. The light generated by this discharge is readily visible at a considerable distance through the end portion of the envelope.

The foregoing disclosure and drawings are merely illustrative of the principles of this invention and are not to be interpreted in a limiting sense. The only limitations are to be determined from the scope of the appended claims.

I claim:

1. A three electrode gas filled discharge device positioned within a transparent envelope comprising, a cylindrical anode, a tubular insulator in axial alignment there with surrounding the anode except for one end where a portion of the anode is exposed, a tubular control electrode surrounding the insulator for a portion of the insulator length, and a fiat disc cathode mounted at right angles to the anode axis with a central hole through which the anode and control electrode extend, said cathode constructed of at least two different metals, one of said metals on the upper cathode surface adjacent to the exposed portion of the anode, the other of said metals covering the rest of the cathode surface and having a work function higher than the work function of the first mentioned metal.

2. A three electrode gas filled discharge device positioned within a transparent envelope comprising, a cylindrical carbon anode, a tubular insulator surrounding the anode except for one end where an exposed portion of the anode extends, said insulator flared at its end adjacent to the exposed portion of the anode, a tubular control electrode surrounding a portion of the insulator, and a flat disc metallic cathode mounted with its surface at right angles to the anode axis with a central hole through which the anode and control electrode extend.

3. A discharge device as set forth in claim 2 wherein said cathode is composed of two metals, a first metal covering substantially all of the cathode surface adjacent to the exposed portion of the anode, and a second metal having a higher work function than the first metal and covering the remaining surface of the cathode, both of said metals insensitive to photon radiation.

4. A discharge device as set forth in claim 3 wherein said first metal is molybdenum and the second metal is nickel.

5. A discharge device as set forth in claim 3 wherein said envelope is filled with a radio-active gas at reduced pressure.

References Qitcd in the file of this patent UNITED STATES PATENTS 2,089,218 Mendenhall Aug. 10, 1937 2,273,958 Holden Feb. 24, 1942 2,331,398 Ingram Oct. 12, 1943 2,340,799 Depp Feb. 1, 1944 2,421,571 Leyshon June 3, 1947 2,525,768 Bruns Oct. 17, 1950 2,646,533 Carne July 21, 1953 2,834,899 Ragosine May 13, 1958 FOREIGN PATENTS 1,075,161 France Apr. 14, 1954 737,386 Great Britain Sept. 28, 1955 805,146 Great Britain Dec. 3, 1958 

